is showing people how to be evil satanic WITCHES. Notice that they call people in the book WITCHES. That is a sign that they are subliminally training people to use WITCHCRAFT. WITCHCRAFT is satanic. Therefore, Harry Potter promotes WITCHCRAFT and YOU SHALL NOT SUFFER A WITCH TO LIVE. Also, the school is called "Hogwarts School of WITCHCRAFT" showing that is obviously teaching people WITCHCRAFT which is SATANIC. In Harry Potter, the WITCHES went to great pains to conceal themselves from the regular, non-satanic folk. This is obviously a secret WITCHCRAFT guide that tells people how to be WITCHES and worship SATAN, while pretending to be an innocent work of fiction. Real WITCHES exist, but they hide well from us using information gleaned from Harry Potter, so that they can continue to worship SATAN.

I've seen numerous such posts before – but that all being said, there is a dreadful fanfic titled My Immortal which actually does have Satan-worshipping protagonists in the Harry Potter universe. I reckon whoever wrote posts as in OP's vein actually took it as serious HP works.